The present invention relates to a method and appara for processing a fine pattern to provide a structure in the unit of an atom or molecule such as film formation and processing of patterns of ultra-fine structures. Examples are the fabrication and correction of ultra-fine patterns such as LSI and patterns of various structures such as molecular devices and bioelements.
The pattern of a semiconductor integrated circuit is becoming more and more fine every year, and the related lithography mask drawing technique, the defect correcting technique and the technique for correcting integrated circuit patterns formed thereby, also have a requirement to become finer.
As to the correction of defects of such mask for lithography, cutting of the internal wiring of the element, the formation of upper and lower wirings, the formation of window and that of jumper wire, there is known a method in which processing such as removal, cutting and perforation are performed using a focused ion beam, and connection, stopgap for forming a take-out electrode and the formation of jumper wire are performed using ion beam induced or laser induced CVD, as disclosed in Japanese Patent Laid-Open Nos. 56332/83, 168652/84 and 229956/87.
With an increase in the degree of degradation of a semiconductor integrated circuit and with the development of molecular electro-elements and molecular bioelectro-elements, patterns are becoming more and more fine. For example, in the case of a mask used in a projection type ion beam lithography or a projection type electron beam lithography, an ultra-fine defect causes a problem. More particularly, for a circuit pattern of 0.3 .mu.m it is necessary to oorrect a defect of 0.07 .mu.m or more, and for a circuit pattern of 0.1 .mu.m it is necessary to correct a defect of 0.02 .mu.m or more. On the other hand, also in a ULSI, in the event of malfunction due to design error or process error, it is necessary to use a correction technique for the cutting or connection of wiring.
In the above prior art, in the case of using an ion beam from a liquid metal ion source, because of a large effective diameter of the ion source which is 20 to 30 nm and because of a large energy width which is several ten eV, the minimum spot diameter has encountered a lower limit of 50 nm or so even when focusing is made at a high magnification using a multi-stage lens. On the other hand, in the case of using an ion source which ionizes H2 gas or Ar gas by electric field ionization at the tip of a needle which has been cooled to an extremely low temperature of about the temperature of liquid He, and then withdraws an ion beam, it is theoretically possible to effect focusing to a minimum of 10 nm or so because the effective diameter of the ion source is as small as one to several atoms at the needle tip and the energy width is as small as one to several eV. However, many extreme conditions are required; for example, an extremely precise technique is required for the production of the needle, and it is necessary to use an ultra-low temperature and a high voltage in ultra-high vacuum. Thus, it is necessary to solve many problems for practical use.
Moreover, molecular electronic elements and bioelectronic elements are under study. The molecular electronics element uses a molecule as a switching element as one limit of element attenuation. The bioelement is constituted by living body related molecules and employs molecules like those in a living body as an information transfer medium by combining molecules of A order having function.
Scanning tunneling microscopes (STM) are known for observation of atoms of a sample and have also been suggested for atomic scale surface modification by atom removal or the like as disclosed in Japanese Patent Application Laid-Open No. 63-92025 having a Laid-Open date of Apr. 4, 1988 and in "Atomic-scale surface modifications using a tunneling microscope", Becker et al, Nature, Vol. 325, Jan. 29, 1987, pp. 419-421. However, such disclosures are not directed to processing of a fine pattern to correct a defect or the like therein or to form a film nor to the processing of molecular devices.
Moreover, such prior art do not disclose a technique capable of performing the correction of defects, cutting and perforation of an ultra-fine pattern not wider than 0.2 .mu.m such as a thin multi-layered film of an inorganic material, as well as processing, movement and adhesion, i.e., repositioning, in the unit of atom or molecule or a group of atoms or molecules in molecular devices using organic high polymers or biopolymers.
It is therefore an object of the present invention to provide a method and apparatus for processing a fine pattern which method and apparatus enable correction of defects of an ultra-fine pattern not wider than 0.2 .mu.m of an electronic device and/or effect operations in the unit of an atom or molecule or a group of atoms or molecules in devices using organic high polymers or biopolymers, and thereby enabling fabrication of a device of ultra-high integration density, a high function device and a device which permits information coupling with living bodies.
In accordance with the present invention, a method and apparatus for processing an ultra-fine pattern utilizes a scanning tunneling microscope system. More specifically, if a scanning tunneling microscope with a needle having a sharp tip is drawn close to a sample surface to be processed at a distance of about 1 nm or less and voltage is applied between the sample and the needle, there will flow a tunnel current therebetween. If the distance is 3 nm or more, there will flow a field emission current. In this case, the tunnel current will flow between the atoms in the needle tip and the sample surface, and the field emission current will spread only several nm on the sample surface because of an extremely short distance. Thus, by various processes using this electric current, processing, alteration or film formation of an ultra-fine pattern, or removing and adding operations in the unit of an atom or molecule are enabled.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for the purposes of illustration only, several embodiments in accordance with the present invention.